One of the greatest problems involved in the use of power chain saws is the so-called "kickback" phenomenon. Kickback is the tendency of a saw to literally throw itself out of the Kerf back toward the operator of the saw. Numerous serious injuries have resulted from chain saw kickback. Indeed, a petition is now pending before the U.S. Consumer Product Safety Commission to establish regulations requiring saw chains to incorporate effective anti-kickback means.
Many attempts have been made to design saw chains which will prevent kickback. Probably the most widely accepted approach is to provide a cam link with an upwardly and rearwardly inclined leading edge preceeding each cutter link to prevent small obstructions from catching against the leading edge of the usual cutter link depth gauge. Examples of such chains are found in Carlton U.S. Pat. No. 3,180,378 and Weiss U.S. Pat. No. 3,910,148. Such chains do reduce the incidence of kickback, but they are only a partial solution to the problem. That is to say, kickback can and does still occur with such chains.
Other attempts at providing a kickback-free chain include Robinson U.S. Pat. No. 3,329,183 which provides a rearwardly projecting tang on the second center link preceeding each cutter link, Anderson U.S. Pat. No. 3,735,662 which discloses a chain utilizing a pair of opposed slitter links followed by a raker link; and Gudmundsen U.S. Pat. No. 2,872,956; Gudmundsen U.S. Pat. No. 2,923,328 and Donley U.S. Pat. No. 2,826,226 which incorporate various types of auxiliary bumper links into the chain.
A particuarly interesting prior art attempt to produce a smooth cutting chain is disclosed in Stihl U.S. Pat. No. 2,963,055 in which a principal depth gauge is mounted on a center link preceeding each cutter link and an auxiliary depth gauge of lesser height is mounted on the cutter link so that as the chain traverses the rounded nose of a saw bar the principal depth gauge pivots out of the way and the effective depth gauge setting of the cutter is increased.
None of the prior art attempts at producing a kickback-free saw chain have been entirely successful. Kickback remains a serious problem for the chain saw industry.